The physical properties of elastomers can some times be improved by blending crystalline polymers therein. For example, the incorporation of syndiotactic-1,2-polybutadiene (SPBD) into rubber compositions which are utilized in the supporting carcass or innerliner of tires greatly improves the green strength of those compositions. The incorporation of SPBD into halogenated butyl rubbers which are utilized as the innerliner compositions for tires also greatly improves the scorch safety of such compositions. U.S. Pat. No. 4,274,462 further disclosed that pneumatic tires having improved resistance against heat build-up can be prepared by utilizing SPBD fibers in their tread base rubber. The green strength of high cis-1,4-polybutadiene can be improved by incorporating a small amount of crystalline trans-1,4-polybutadiene therein. These are just a few examples of improved properties which can be attained by dispersing crystalline polymers throughout rubbery elastomers.
Such blends of crystalline polymers with rubbery elastomers are typically prepared utilizing standard mixing techniques. For instance, the crystalline polymer could be mixed throughout the rubbery elastomer utilizing a Banbury mixer or a mill mixer. However, these standard mixing procedures have certain drawbacks. These drawbacks include high processing costs, polymer degradation, inadequate mixing, and process limitations. The processing equipment required in order to mix crystalline polymers throughout rubbery elastomers by mastication is expensive and very costly to operate. Such standard mixing procedures result in polymer degradation due to the high shearing forces and high temperatures which may be required for mixing. For instance, it is generally desirable to mix the crystalline polymer throughout the rubbery elastomer at a temperature which is above the melting point of the crystalline polymer. Accordingly, SPBD powder, which is utilized in tire innerliner or carcass compounds, is mixed into the compound utilizing standard mixing procedures at a temperature which is at least as high as the melting point of the SPBD being used. Since high mixing temperatures result in degradation of the rubbery elastomer being utilized as the innerliner or carcass compound, the melting point of the SPBD utilized has typically been limited to no more than about 190.degree. C. In order to limit polymer degradation, the SPBD utilized in such applications typically has a melting point of no more than about 160.degree. C. Even though the green strength of tire carcass compounds containing SPBD increases with the melting temperature of the SPBD, the higher mixing temperature associated with the higher melting SPBD makes its utilization very difficult because of the degradation that occurs utilizing standard mixing techniques. Furthermore, good dispersions of SPBD throughout rubbers are difficult to attain utilizing conventional mixing techniques.